Identification of a Rotating Sound Source in a Duct with High Spatial Resolution
Invited paper
KAIST
Wednesday 3 june, 2015, 14:40 - 15:00
0.3 Copenhagen (49)
Abstract:
Spatial distribution of acoustic parameters at the source plane provides
important information for development or refinement of quiet in-duct fluid
machines. Inverse estimation techniques using measured in-duct pressures and
sound propagation models can be used for source identification. However, when
the acoustic source is rotating, it is not easy to identify the source
parameter distribution clearly in source planes of complicated shapes. In this
work, a method is suggested for identifying rotating noise sources in a duct
with a reasonable spatial resolution. For obtaining detailed information about
the source distribution, evanescent waves are included in the propagation
model based on the modal summation method. The Doppler effect caused by source
rotation is also considered in the modeling. For validating the suggested
method, an experiment is conducted in a duct system with a rotating
loudspeaker, which radiates a pure tone, in the absence of flow. The measured
near-field pressure shows the shift of spectral peaks due to the Doppler
effect. The modal amplitudes related to the rotation of loudspeaker are
estimated to obtain the source parameters. The near-field sound pressure is
regenerated from the estimated modal amplitudes, giving a maximum error less
than -10 dB. The pressure and velocity fields over the source plane are
calculated using the estimated modal amplitudes. The reconstructed result
clearly indicates the rotating loudspeaker as the main noise source in the
rotating reference frame.